Carbohydrate - DOC by 9BM6wzi5

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									Carbohydrates Lab                                                          Page 1 of 8


Name of Each Member of The Group:




Pre-Lab: (To be completed before start of Lab)

   1. Draw Fischer projections of L-Glyceraldehyde and D-Glyceraldehyde:




   2. What is the relationship between L-Glyceraldehyde and D-Glyceraldehyde?




   3. Draw the Fischer projection for D-Glucose:




   4. Draw the Haworth projections for α-D-Glucose and β-D-Glucose:




   5. Draw the Haworth projection for α-D-Maltose:




   6. Draw the Haworth projection for α-D-Sucrose:
Carbohydrates Lab                                                             Page 2 of 8


   7. Draw the Haworth projection for Amylose:




   8. What carbohydrate(s) would you expect to produce a reddish-orange solid with
      Benedict’s Solution and a red color with Seliwanoff’s Reagent in about a minute?

              Glucose / Fructose / Sucrose / Lactose / Starch / Water


   9. What carbohydrate(s) would you expect not to produce a color with Benedict’s
      Solution but to turn a blue-black color with the iodine reagent?

              Glucose / Fructose / Sucrose / Lactose / Starch / Water


   10. What carbohydrate(s) would you expect not to produce a color with Benedict’s
       Solution, turn a light orange color with Seliwanoff’s Reagent after 5 minutes, and
       not produce any bubbles during fermentation?

              Glucose / Fructose / Sucrose / Lactose / Starch / Water




                 END OF PRE – LAB
              (To be turned in along with
             Results Table and Questions)
Carbohydrates Lab                                                               Page 3 of 8


Objectives:

This lab will review structures of mono-, di-, and polysaccharides and will investigate the
properties of carbohydrates using a number of analytical tests.

Materials Needed:

              Equipment                                       Chemicals
Molecular Model Kit                           2% Glucose Solution
Test Tube Rack                                2% Fructose Solution
Test Tubes                                    2% Sucrose Solution
400 mL Beaker                                 2% Lactose Solution
10 mL Graduated Cylinder                      2% Starch Solution
Hot Plate                                     Benedict’s Solution
Droppers                                      Seliwanoff’s Solution
Litmus Paper                                  Iodine Solution
                                              10% HCl Acid
                                              10% NaOH Base
                                              Yeast

Discussion:

Carbohydrates are the main source of energy in our diets. Carbohydrates are organized
into three categories: monosaccharides, disaccharides and polysaccharides.
Monosaccharides are the simplest carbohydrates and cannot be hydrolyzed into smaller
units. They can be further classified as either aldoses (e.g. glucose) or as ketoses (e.g.
fructose). All monosaccharides follow the chemical formula: CnH2nOn.
Monosaccharides can form cyclic structures that contain a hemiacetal functional group.
Whether a monosaccharide exists as its open structure or as its cyclic structure (as a
hemiacetal), it can be oxidized. Sugars that can be oxidized are referred to as reducing
sugars.

Disaccharides are formed when two monosaccharides join together by a glycosidic
bond. Common disaccharides include: sucrose, lactose and maltose. Both lactose and
maltose are formed with one of the monosaccharide units remaining as a hemiacetal;
whereas, sucrose is formed when each of the hemiacetal functional groups react with
each other forming an acetal. Acetals cannot open, and sucrose is not a reducing sugar.

Polysaccharides are very long polymer chains of glucose molecules. Starches are
polysaccharides that are connected by alpha glycosidic bonds and cellulose is a
polysaccharides joined by beta glycosidic bonds. All polysaccharides are polymers of
glucose.

In this experiment, we will look at the structure of mono-, di-, and polysaccharides. We
will also use several chemical tests to determine structural features.
Carbohydrates Lab                                                              Page 4 of 8


Benedict’s Test

All monosaccharides and some disaccharides can be oxidized, and are therefore called
reducing sugars. Benedict’s solution contains copper(II) ions. When a sugar is oxidized,
the copper(II) ions are reduced to copper(I) ions. It is more obvious that aldoses are
reducing sugars, since they contain an aldehyde group, which is oxidized to a carboxylic
acid group. It is not as obvious why ketoses are also reducing sugars. The fact that
ketoses can isomerizes into aldoses when dissolved in water is the reason why even
ketoses are reducing sugars. A positive Benedict’s test is observed when the blue
copper(II) ions are reduced to a reddish-orange precipitate of copper(I) oxide or a
greenish color of free copper(I) ions.

Seliwanoff’s Test

Seliwanoff’s test will distinguish between aldoses and ketoses. When Seliwanoff’s reagent
is mixed with a ketose, a deep red color forms rapidly. When mixed with an aldose, a
light pink color will form slowly.

Iodine Test

When amylase (a starch) is mixed with iodine, the polysaccharide changes shape and
traps the iodine molecules. The complex formed is a deep blue-black color.
Amylopectin, cellulose and glycogen react with iodine to form red to brown colors.
Monosaccharides and disaccharides do not react with iodine at all.

Hydrolysis

Disacchardies can be readily hydrolyzed (cleaved by water) into monosaccharides in the
presence of an acid. Starches are much more difficult to hydrolyze and are first broken
down into smaller polysaccharides or disaccharides, which are in turn hydrolyzed to
monosaccharides. Complete hydrolysis of polysaccharides results in the formation of
glucose. In our bodies, the enzyme amylase and maltase are responsible for the
breakdown of polysaccharides.

Fermentation

Although yeast can contain many enzymes, commercial yeast available today has been
developed for household use and has been selected to be effective with sucrose and
glucose for cooking purposes. In the past, yeast contained enough maltase to hydrolyze
maltose into glucose and would give a positive fermentation test with maltose. It is not a
common result with current yeast, but it is possible. Signs of fermentation are bubbles
of carbon dioxide forming and rising to the top of the test tube.
Carbohydrates Lab                                                             Page 5 of 8


Procedures:

   1.   Have the Pre-Lab checked before beginning.
   2.   Fill out the results table of expected results before beginning lab work.
   3.   Procure an UNKNOWN and a FOOD Item before beginning lab work.
   4.   Begin the Tests: (Start with the Fermentation Test as it takes time)

Benedict’s Test

   1. Place 10 drops of a 2% solution of glucose, fructose, sucrose, lactose, starch and
      water into separate test tubes. Label each tube with a marker.
   2. Add 2 mL of Benedict’s solution to each test tube.
   3. Place each test tube into a hot water bath (400 mL beaker filled about half way
      with boiling water on a hot plate) for 3 – 5 minutes.
   4. Observe and record any changes in color. Note that the water is used as a
      control and should not react with Benedict’s solution.

Seliwanoff’s Test

   1. Place 10 drops of a 2% solution of glucose, fructose, sucrose, lactose, starch and
      water into separate test tubes. Label each tube with a marker.
   2. Add 2 mL of Seliwanoff’s solution to each test tube with caution as it contains
      concentrated HCl acid.
   3. Place each test tube into a hot water bath (400 mL beaker filled about half way
      with boiling water on a hot plate) and note the time.
   4. After 1 minute, observe and record color changes as fast, slow or no change.

Iodine Test

   1. Place 5 drops of a 2% solution of glucose, fructose, sucrose, lactose, starch and
      water into separate test tubes. Label each tube with a marker.
   2. Add 1 drop of iodine solution to each test tube.
   3. Observe and record any color changes.

Fermentation Test

   1. Setup a fermentation test tube for each of the carbohydrate solutions. Yeast will
      be added to each tube and at the end of the lab period, observe and record any
      gas bubbles that may have formed.

UNKNOWN and FOOD Test

   1. On the Unknown and Food samples, perform: Benedict’s, Seliwanoff’s iodine
      tests and fermentation tests.
   2. Record all observations.
Carbohydrates Lab                                                           Page 6 of 8


Hydrolysis of Di- and Polysaccharides:

   1. Add 3 mL of 2% starch solution into two test tubes and label.
   2. Add 3 mL of a 2% sucrose solution into two different test tubes and label.
   3. To one sample each of both the starch and sucrose, add 20 drops of 10% HCl
      acid. Add to the labels an ‘ACID’ designation.
   4. To the other, untouched, set of starch and sucrose test tubes add 20 drops of
      water. Add to the labels an ‘WATER designation.
   5. Heat all four of these test tubes in boiling water for 10 minutes.
   6. Remove the test tubes and allow to cool to room temperature.
   7. To the test tubes containing the HCl acid, add 10% NaOH (about 20 drops) until
      litmus turns blue, showing that the HCl has been neutralized.
   8. Test each of the samples as follows:
          a. Iodine Test: Place 5 drops of each test tubes contents into a fresh test
              tubes and label. To each of add 1 drop of iodine solution to each of
              these test tubes just made. Observe and record any changes in color.
          b. Add 2 mL of Benedict’s solution to each of the remaining samples. Heat
              each test tube in boiling water for 3 – 5 minutes. Observe and record any
              changes in color.
Carbohydrates Lab                                                                                       Page 7 of 8


Results Table

                                UNKNOWN: __________________


                                FOOD ITEM: __________________

           Benedict’s Test            Seliwanoff’s Test          Iodine Test                Fermentation
           What you    Actual         What you    Actual         What you    Actual         What you       Actual
           expect      Observations   expect      Observations   expect      Observations   expect         Observations
           BEFORE                     BEFORE                     BEFORE                     BEFORE
           Beginning                  Beginning                  Beginning                  Beginning
           the Lab                    the Lab                    the Lab                    the Lab
Glucose



Fructose



Sucrose



Lactose



Starch



Water



Unknown



Food
Carbohydrates Lab                                                            Page 8 of 8


Results Continued

Hydrolysis of Di- and Polysaccharides

Solution              Iodine Test            Benedict’s Test       Possible Hydrolysis
                                                                   Products
Sucrose + HCl
Sucrose + H2O
Starch + HCl
Starch + H2O

Questions

   1. How do the results from the iodine test indicate whether hydrolysis has
      occurred during the hydrolysis portion of the lab?




   2. How do the results from the Benedict’s test indicate whether hydrolysis has
      occurred during the hydrolysis portion of the lab?




   3. Based on the results what carbohydrate(s) could possibly be in your:
         a. The UNKNOWN




           b. Your FOOD ITEM




                              END OF LAB
Please turn in the following items for this lab: (One per Group)
     Pre Lab (Both pages) with names in the box
     Results Table
     Questions

								
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